The invention relates to an inking unit, particularly for an offset printing machine, having a first smoothing roller, an ink feed unit formed as a droplet generator for applying a metered quantity of ink indirectly via an additional roller interposing the ink feed unit and the first smoothing roller, or directly, to the first smoothing roller, and a second smoothing roller operatively connected to the first smoothing roller for distributing the applied ink.
Inking units of the type mentioned at the introduction hereto have become known heretofore. It is disadvantageous that, with inking units of this type, a locally, relatively intensive accumulation of ink on a first smoothing roller is not completely evened out. In this regard, a locally limited and intensive accumulation of ink, which is also referred to as an xe2x80x9cink dotxe2x80x9d, is produced by an application of ink to a smoothing roller, for example, by a valve technique already known heretofore. The published German Patent Document DE 43 27 212 A1 describes a transfer of ink in the printing unit of an offset printing machine by a digitally controllable ink jet printing apparatus, and the published German Patent Document DE 44 05 912 A1 is concerned with a contact-free application of ink to rotating printing systems. By the valve technique, it is possible to transfer an offset ink in a pulse-like manner in the form of small drops or droplets to a smoothing roller of an inking unit of an offset printing machine utilizing digital control. In this regard, what is involved is a virtually point-like application of ink to a smoothing roller, the extent of the ink application being considerably smaller than the nominal size of an inking area to be implemented or realized by the inking unit. It is disadvantageous that such locally limited, point-like accumulations of ink are visible on a printed paper sheet. The cause of such a qualitative restriction on the offset printing result is the aforementioned inadequate evening-out of the locally limited accumulation of ink (ink dot) by conventional offset inking units.
It is accordingly an object of the invention to provide an inking unit, particularly of an offset printing machine, which, in a relatively simple and reliable manner, achieves an evening-out of a locally limited accumulation of ink on a smoothing roller, especially of an offset inking unit, which is sufficient to improve the printing quality.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, an inking unit, comprising a first smoothing roller, an ink feed unit constructed as an ink droplet generator for applying a metered quantity of ink to the first smoothing roller, by one of an indirect and a direct path, respectively, the indirect path being via at least one additional roller interposing the ink feed unit and the first smoothing roller, and the direct path being directly to the first smoothing roller, and further comprising a second smoothing roller operatively connected to the first smoothing roller for distributing the application of ink, each of the first and the second smoothing rollers having a hard smoothing surface with a hardness of one of at least 80 Shore A and at least 30 Shore D, respectively, for forming a uniform film of ink.
In accordance with another feature of the invention, the respective smoothing surface is formed of a substance selected from the group thereof consisting of hard rubber, polyurethane and the composition known by the trade name Rilsan, respectively.
In accordance with a further feature of the invention, the ink feed unit is an inkjet device.
In accordance with an added feature of the invention, the second smoothing roller is operatively connected to a supporting roller.
In accordance with an additional feature of the invention, the smoothing surfaces have a hardness of 95 Shore A.
In accordance with yet another feature of the invention, the supporting roller has a supporting surface with a hardness of less than 60 Shore A.
In accordance with yet a further feature of the invention, the supporting roller has a supporting surface with a hardness of 25 Shore A.
In accordance with yet an added feature of the invention, at least one additional smoothing roller having a smoothing surface and disposed at a spaced distance from the second smoothing roller is in operative connection with the first smoothing roller.
In accordance with yet an additional feature of the invention, after the ink has been applied, the additional smoothing roller is disposed downline from the second smoothing roller, as viewed in the direction of rotation of the first smoothing roller.
In accordance with still another feature of the invention, the smoothing surface of the additional smoothing roller is a comparatively hard smoothing surface and has a hardness of one of at least 80 Shore A and at least 30 Shore D, respectively.
In accordance with still a further feature of the invention, the smoothing surface of the additional smoothing roller has a hardness of 95 Shore A.
In accordance with still an added feature of the invention, the smoothing surface of the additional smoothing roller is a comparatively soft smoothing surface and has a hardness of less than 60 Shore A.
In accordance with still an additional feature of the invention, the smoothing surface of the additional smoothing roller has a hardness of 25 Shore A.
In accordance with another aspect of the invention, there is provided an inking unit, comprising a first smoothing roller, an ink feed unit constructed as an ink droplet generator for applying a metered quantity of ink to the first smoothing roller, by one of an indirect and a direct path, respectively, the indirect path being via at least one additional roller interposing the ink feed unit and the first smoothing roller, and the direct path being directly to the first smoothing roller, and further comprising at least one additional smoothing roller operatively connected to the first smoothing roller for distributing the application of ink, the first smoothing roller having a hard smoothing surface with a hardness of one of at least 80 Shore A and at least 30 Shore D, respectively, and the at least one additional smoothing roller having a soft smoothing surface of less than 60 Shore A, for forming a uniform film of ink.
In accordance with a further aspect of the invention, there is provided an inking unit, comprising a first smoothing roller, an ink feed unit constructed as an ink droplet generator for applying a metered quantity of ink to the first smoothing roller, by one of an indirect and a direct path, respectively, the indirect path being via at least one additional roller interposing the ink feed unit and the first smoothing roller, and the direct path being directly to the first smoothing roller, and further comprising a second smoothing roller operatively connected to the first smoothing roller for distributing the application of ink, and a drive for rotationally driving the second smoothing roller at a circumferential speed differing from the circumferential speed of the first smoothing roller, for forming a uniform film of ink.
In accordance with an added aspect of the invention, there is provided an offset printing machine having an inking unit comprising a first smoothing roller, an ink feed unit constructed as an ink droplet generator for applying a metered quantity of ink to the first smoothing roller, by one of an indirect and a direct path, respectively, the indirect path being via at least one additional roller interposing the ink feed unit and the first smoothing roller, and the direct path being directly to the first smoothing roller, and further comprising a second smoothing roller operatively connected to the first smoothing roller for distributing the application of ink, each of the first and the second smoothing rollers having a hard smoothing surface with a hardness of one of at least 80 Shore A and at least 30 Shore D, respectively, for forming a uniform film of ink.
In accordance with an additional aspect of the invention, there is provided an offset printing machine having an inking unit, comprising a first smoothing roller, an ink feed unit constructed as an ink droplet generator for applying a metered quantity of ink to the first smoothing roller, by one of an indirect and a direct path, respectively, the indirect path being via at least one additional roller interposing the ink feed unit and the first smoothing roller, and the direct path being directly to the first smoothing roller, and further comprising at least one additional smoothing roller operatively connected to the first smoothing roller for distributing the application of ink, the first smoothing roller having a hard smoothing surface with a hardness of one of at least 80 Shore A and at least 30 Shore D, respectively, and the at least one additional smoothing roller having a soft smoothing surface of less than 60 Shore A, for forming a uniform film of ink.
In accordance with yet another aspect of the invention, there is provided an offset printing machine having an inking unit, comprising a first smoothing roller, an ink feed unit constructed as an ink droplet generator for applying a metered quantity of ink to the first smoothing roller, by one of an indirect and a direct path, respectively, the indirect path being via at least one additional roller interposing the ink feed unit and the first smoothing roller, and the direct path being directly to the first smoothing roller, and further comprising a second smoothing roller operatively connected to the first smoothing roller for distributing the application of ink, and a drive for rotationally driving the second smoothing roller at a circumferential speed differing from the circumferential speed of the first smoothing roller, for forming a uniform film of ink.
In accordance with a concomitant feature of the invention, the inking unit is of an offset printing machine.
The aforementioned object of the invention is thus achieved by providing an inking unit wherein, for forming a uniform film of ink, the first and second smoothing rollers each have a hard smoothing surface with a hardness which is at least 80 Shore A or at least 30 Shore D.
Heretoforeknown offset inking units have pairs of rollers with operative surface connections which are characterized by a hard/soft or soft/soft category. Because of the relatively high hydrodynamic pressure which is established in the respective nip, and also the low hardness of the soft surfaces (rubber with a low elastomer stiffness), a metered, locally limited application of ink (ink dot) is not sufficiently smoothed or evened out by such pairings of rollers.
By providing a roller pairing according to the invention having an operative surface connection of the hard/hard category, the evening out of locally limited, intensive accumulations of ink in an offset inking unit, which is sufficient to ensure a reproducible improvement in the printing quality, is achieved in a relatively simple and reliable manner. Therefore, by the roller pairing with the operative surface connection hard/hard, a sufficiently evened out film of ink is produced from an ink dot and can then be processed further by an inking unit of otherwise conventional construction. The achieved evening-out effect results primarily from the ink dot being rolled out in the circumferential direction of the rollers, with a considerable reduction in the height of the ink dot and, to a secondary extent, by the application of ink being distributed by rubbing on the surfaces of the rollers. The smoothing surfaces each have a hardness of at least 80 Shore A or at least 30 Shore D. By these hardness values, optimized results can be achieved with regard to evening out locally limited accumulations of ink.
The respective smoothing surface is advantageously formed of hard rubber or polyurethane or the aforementioned substance having the trade name Rilsan. These materials are particularly suitable for producing a hard smoothing surface.
The ink feed unit is preferably a droplet generator in the form of an inkjet device. An ink feed unit constructed in this way is particularly suitable for contact-free application of ink, forming an ink dot on a smoothing roller. This ink feed unit therefore uses valve technology.
According to another embodiment, the ink feed unit is operatively connected directly to the first smoothing roller. This permits the inking unit to have a compact configuration, at least in the region of ink application by the ink feed unit, because the application of ink takes place directly from the ink feed unit to the first smoothing roller.
According to an alternative embodiment, the ink feed unit is operatively connected indirectly to the first smoothing roller, with the interposition of a single additional roller or a plurality of additional rollers. For example, the single additional roller or one of the additional rollers, respectively, may be formed by the second smoothing roller which, in this case, finds a multifunctional use. By such an indirect application of ink, further optimization with regard to evening out the ink dot on the first smoothing roller can be achieved, if necessary or desirable.
The second smoothing roller is preferably operatively connected to a supporting roller. The supporting roller is used for preventing the second smoothing roller from bending due to the relatively high hydrodynamic pressure which is established between the two smoothing rollers. In this regard, the supporting roller can have a soft surface covering.
The smoothing surfaces advantageously have a hardness of 95 Shore A, and the supporting roller has a supporting surface with a hardness of less than 60 Shore A and, in particular, of about 25 Shore A. By these hardness values, unwanted bending of the second smoothing roller due to the relatively high hydrodynamic pressure that is established in the nip between the two smoothing rollers is avoided, and therefore optimized evening out of the application of ink on the first smoothing roller is achieved.
According to a further development, at least one additional smoothing roller with a hard smoothing surface is operatively connected to the first smoothing roller, at a spaced distance from the second smoothing roller. Such an arrangement is advantageous, in particular, in a shortened inking unit, because, in a shortened inking unit, a lower number of roller pairings is provided, so that through the intermediary of an additional smoothing roller, operatively connected to and parallel to the first smoothing roller, correct evening out of the application of ink can be achieved in a reliable and flexible manner, even in a shorter inking unit.
The additional smoothing roller is advantageously arranged downline of the second smoothing roller, as viewed in the direction of rotation of the first smoothing roller, after the ink has been applied. In this way, through the intermediary of the additional smoothing roller, the result already achieved by the operative connection between the first and the second smoothing roller can be optimized with regard to adequate evening out of the application of ink.
According to a further development, to form a uniform film of ink, the second smoothing roller is driven rotationally by a drive with a circumferential surface speed that differs from that of the first smoothing roller. By producing a differential speed of this type between the first and the second smoothing roller, slippage is produced in the contact area therebetween. With the aid of sufficiently high slippage, the local accumulation of ink is rolled out and, in particular, an xe2x80x9cink peakxe2x80x9d which may be present is removed. In this way, with the aid of axial frictional distribution and in cooperation with further inking rollers in an inking unit (roll stand), uniform application of ink is advantageously obtained. In this regard, the realization of a desired differential speed between the first and the second smoothing rollers is performed by a suitable drive, for example, in the form of an appropriately constructed gear drive, or a direct drive via a separate drive motor.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an inking unit, especially for an offset printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: